In these days, liquid crystal display devices are widely and commonly used as devices for displaying letters and images. In particular, liquid crystal display devices that are provided with a liquid crystal display panel of the active matrix type, in which a desired pixel is turned on/off by performing on/off control of a switching device (such as a TFT [thin film transistor]) formed in each pixel, have become the mainstream of liquid crystal display devices because of its high contrast performance and its high-speed display performance.
FIG. 9 is a circuit diagram showing an example of a conventional source driver that applies a source voltage VS to a liquid crystal display panel of the active matrix type.
As shown in FIG. 9, the conventional source driver generates a twice-boosted voltage 2VDDH (e.g., 5.6 [V]) from a supply voltage VDDH (e.g., 2.8 [V]) supplied from outside, and then, by use of this, drives a source amplifier AMP 1 to generate a source voltage VS (e.g., 0 to 4 [V]) corresponding to a halftone value (e.g., 0 to 255) of input data, and then applies it to the liquid crystal display panel (in FIG. 9, a panel load Z).
FIG. 10 is a diagram illustrating the conventional pulse drive of the source voltage VS. In an upper part of the diagram, there are shown a gate voltage application period and a source voltage application period in a first horizontal period 1H in an Nth frame and in an (N+1)th frame; in a lower part, the voltage waveform of the source voltage VS is shown.
As shown in FIG. 10, the conventional source driver applies the source voltage VS from the source amplifier AMP1 to the liquid crystal display panel through out the gate selection period.
FIG. 11 is a circuit diagram showing an example of a conventional common driver that applies a common voltage VCOM to the liquid crystal display panel of the active matrix type.
As shown in FIG. 11, the conventional common driver has a positive common amplifier AMP2 generating a predetermined positive voltage VCOMH (e.g., 3.6 [V]) by use of the boosted voltage 2VDDH, and a negative common amplifier AMP3 generating a negative voltage VCOML (e.g., −1 [V]) by use of the supply voltage VDDH, in which one of the positive voltage VCOMH, a reference voltage VSS (a ground voltage GND), and the negative voltage VCOML is selectively applied so that the polarity of the common voltage VCOM is reversed at every horizontal period (e.g., 40 to 50 [<s]) (a so-called common AC drive system).
For example, in a 2.2 inch QVGA [quarter video graphics array] liquid crystal display panel, a load capacity of about 11 [nF] is periodically applied with the common voltage VCOM with an amplitude of about 5 [V], so that the load capacity is repeatedly charged and discharged.
FIG. 12 is a diagram illustrating the conventional pulse drive of the common voltage VCOM, and shows the voltage waveform of the common voltage VCOM.
As shown in FIG. 12, the conventional common driver has ternary drive system in which the reference voltage VSS (the ground voltage GND) is gone through on high-level transition and low-level transition of the common voltage VCOM.
As an example of a conventional technology related to the above description, Patent Document 1 discloses a drive circuit for a liquid crystal display device that includes multiple-value voltage generation means generating a plurality of voltages; a selection circuit selecting, from the voltages generated by the multiple-value voltage generation means, a voltage required for driving; and an output circuit is fed with the voltage selected by the selection circuit and outputting a desired voltage to a drive circuit output terminal, in which the output circuit includes an output circuit input terminal to which the voltage selected by the selection circuit is fed; the drive circuit output terminal; a first voltage source; a second voltage source; a first switch connected between the output circuit input terminal and the drive circuit output terminal; a transistor of which the drain is connected to the first voltage source, the gate is connected to the output circuit input terminal, and the source is connected to the drive circuit output terminal; and a second switch connected in between the drive circuit output terminal and the second voltage source.    Patent Document 1: JP-A-10-301539 Publication